Reliable measurement of silo levels is an important prerequisite for efficient production in mills and large bakeries. But the measurements are not always easy. Extremely narrow silos, high dust development and changing products demanded everything from the implemented level measuring instruments. The new Vegapuls 69 radar level measuring instrument now ensures more reliable measured data and considerably simplifies measurement.
Modern radar sensors that were developed especially for the requirements of the bulk solids industry show their strengths in many areas of application in the grain processing industry. They supply reliable measuring results for many different products uninfluenced by extreme dust development.
The products in a mill are very varied and range from different kinds of grain and fine flour dust to sub-products such as bran. The products are usually stored in high, slim silos to concentrate a high filling volume in a compact area and to store as wide a variety as possible. Increasingly higher silos are being used in order to store the large number of products as space-savingly as possible. This often brings the previously used measuring principles up to their physical limits.
For large bakeries and bulk buyers, the mill often takes over the monitoring of product stocks and is responsible for on-time delivery of the material. A reliable level measurement in the different silos is essential for planning logistics exactly. In modern plants the level data are collected by central processing systems and put directly on the Internet or sent by e-mail. This enables the mill to constantly ensure optimum stocks for their customers and to optimise the product delivery by the appropriate route planning.
The crux of this silo management is the reliable measurement of the contents of the silos because only then is exact planning possible. However, the very different properties of the products place great demands on the used measuring principle. This frequently led to problems in the past.
Reliable monitoring – Modern measuring principles such as free-radiating and guided radar now open up new opportunities for reliable monitoring of the silo levels in the mill. Non-contact radar technology especially has essential advantages in the grain silo. The radar sensor supplies an accurate measuring result regardless of the dust and noise development or air turbulences. By good focusing of the microwaves and the use of a swivel holder, the measuring signal can be aimed exactly at the product surface. Fluctuations of the product properties such as the moisture content or the degree of maturity have no influence on the measuring result. However, only a fraction of the energy is reflected at the product surface of many grain products because of the low dielectric figure. The result is very small measuring signals which almost disappear under the noise. Together with interference signals from installations this leads to uncertain measuring signals. Modern software and algorithms do a lot to help but sometimes the physics simply has its limits.
Focus on exact measured values – It is for such measurements that the Schiltach company Vega has developed the Vegapuls 69 which is being launched at the Powtech 2014. The new radar sensor operates with a frequency of 79 GHz with which a much higher focusing of the transmission signal is possible. The good focusing helps above all for better distinction of the actual measuring signal from interference signals in narrow containers with installations. The new microwave components can measure even the smallest reflection signals. This benefits all applications which previously supplied very small reflections such as bran. A reliable level measurement of bran is very difficult because of the very low bulk weight and the extremely low dielectric figure. Almost all conventional measuring methods meet their match here.
Typical grain containers are high and narrow (sometimes only 1 m x 1 m) or divided into different segments. An ideal application site for the new level measuring instrument. Thanks to the very good signal focusing, measurement is possible in a more than 15 m high fodder silo with a base area of 1 m2 . The VEGAPULS 69 reliably measures the filling height of the medium. This is above all due to the small opening angle. The opening angle of the radiated radar energy and thus the focusing depends on two factors: The transmission frequency and the active antenna area. This means that a much better focusing is achieved at a higher frequency with the same antenna size. The Vegapuls 69 operates with a transmission frequency of 79 GHz and an antenna size of 75 mm. This achieves an opening angle of less than 4°. By comparison: In a radar sensor with a transmission frequency of 26 GHz the opening angle is about 10° with the same antenna size. The 79 GHz beam misses installations or deposits on the container wall, making the measurement more accurate and reliable. The better focusing also allows measurement into the discharge hopper – this improves utilisation of the silo.
Optimal integration into the systems – The sensor directly supplies an output signal of 4 … 20 mA proportional to the level which can be integrated into existing evaluation systems. Wiring is reduced to a minimum by the user-friendly 2-wire technology. The sensors are approved for use in areas with a dust explosion hazard and can therefore be used in all areas in which organic dusts occur.
For complex container shapes, the container geometry can be stored in the sensor and an output signal proportional to volume or weight can be obtained directly. The measured value display and operation take place directly on the sensor or conveniently with a remote display.
Together with a continuous measurement, sensors for point level detection (Vegavib, Vegawave, Vegacap) offer additional safety as an independent measuring system. For further processing of the measured values, VEGA offers a wide range of signal conditioning instruments from the simple display to linking to Ethernet and measured data wireless transmission. The Vega Inventory System enables optimum logistics of raw materials from the supplier to the production facility.
Summary and forecast – In addition to better focusing and higher dynamics, the Vegapuls 69 also features a much wider range of application. The universal application possibilities of the sensor offer important advantages especially in applications in which very different media are stored. The silo cells in the grain processing industry, for example, are often filled with different products with quite different reflection properties. Wheat, corn or also bran is stored in the silos as required. Measuring these different media with a single level measuring instrument was often a challenge for the measuring technology. The wide range of application of the new Vegapuls 69 also meets these requirements. With a measuring range of up to 120 m and an accuracy of ±5 mm, the Vegapuls 69 also offers enough power reserves – accurate measuring results are achieved even in high silos.
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